1. Field of the Invention
The present invention relates to wireless universal serial bus (WUSB) security, and more particularly to, a method and apparatus for providing a session key for WUSB security and a method and apparatus for obtaining the session key.
2. Description of the Related Art
After a universal serial bus (USB) that connects a computer and its peripheral devices was popularized, a wireless universal serial bus (WUSB) that supports the USB wirelessly was introduced because of the popularity the wireless LAN.
FIG. 1 is a diagram of a conventional WUSB system. Referring to FIG. 1, the conventional WUSB system comprises a host 2, devices 1˜3 (or 31˜33), and a guest device 34.
The host 2 is a computer system serving as a WUSB host. The devices 1˜3 (or 31˜33) and the guest device 34 are peripheral devices serving as WUSB devices, e.g., a WUSB keyboard, a printer, an external storage unit, a digital camera, etc. In particular, the devices 1˜3 (or 31˜33) are continuously connected to the host 2 and the guest device 34 is connected temporarily to the host 2 by a user.
According to WUSB standards, the host 2 generates a connection context (CC) necessary for creating a session key during a session between the host 2 and the guest device 34. The user distributes the session key to the guest device 34. The session key is called a pair-wise temporal key (PTK).
FIG. 2 is a flowchart of a conventional WUSB security communication method. Referring to FIG. 2, the host 2 generates the CC including a connection host ID (CHID), a connection device ID (CDID), and a seed key connection key (CK), and outputs the CC to a user 1 (Operation 201).
The user 1 distributes the CC to the guest device 34 connected to the host 2. The user 1 sees the CC output by the host 2, and inputs the CC to the guest device 34 using an input tool such as a keyboard. Alternatively, the user downloads the CC output by the host 2 in a recording medium such as a CD ROM, and uploads the downloaded CC to the guest device 34 (Operation 202).
The guest device 34 provides the CDID to the host 2 to request a connection with the host 2, and the host 2 transmits a response indicating that the guest device 34 is connected to the host 2 of the guest device 34 (Operation 203).
According to the WUSB standards, the host 2 and the guest device 34 exchange four messages with each other to obtain information necessary for creating a session key. A message exchange protocol is called a 4-way handshake.
Throughout the specification, HNonce and DNonce are random numbers. HNonce corresponds to a device and DNonce corresponds to a device or more often a guest device in the specification. TKID is the information for identifying the session key throughout the specification. The host 2 transmits a message M1 including information for identifying the session key, TKID, and a HNonce to the guest device 34 (Operation 204).
The guest device 34 generates a DNonce (Operation 205).
The guest device 34 creates a session key corresponding to the TKID based on the address of the host 2, the address of the guest device 34, the HNonce, the DNonce, and the SEED KEY CK (Operation 206).
The guest device 34 transmits a message M2 including the TKID and the DNonce to the host 2 (Operation 207).
The host 2 creates the session key corresponding to the TKID based on the address of the host 2, the address of the guest device 34, the HNonce, the DNonce, and the SEED KEY CK (Operation 208).
The host 2 calculates a message integrity code (MIC). Then, the host 2 transmits a message M3 including the TKID, the DNonce, and the MIC to the guest device 34 (Operation 209).
The guest device 34 calculates a MIC, if the MIC is identical to the MIC obtained from the host 2, installs the session key, and transmits a message M4 indicating the session key is successfully installed to the host 2 (Operation 210).
The guest device 34 performs secured communications with the host 2 using the session key during a session (Operation 211).
The host 2 deletes the CC regarding the guest device 34, and releases the session between the host 2 and the guest device 34 (Operation 212).
Information necessary for creating the session key (i.e., information corresponding to the CC), must be shared by the host 2 and the guest device 34 to perform secured communications using the session key. However, according to the WUSB standards, whenever a guest device is connected to the host 2, the user 1 distributes information necessary for creating the session key to the guest device, which is very burdensome to the user 1. In particular, the user 1 is burdened if guest devices are frequently connected to the host 2, resulting in decreased user convenience which is the purpose of WUSB.
According to the WUSB standards, since the user 1 must update the CC whenever a guest device is connected to the host 2, the entire WUSB system including a host and devices that share the CC must be updated, which gives a considerable load to the host and devices.